Laboratory cell culture is a biological technique used to grow cells, bacteria, etc. under sterile conditions. It is typically performed using a petri dish or culture bottle filled with a small volume of nutrient media and placed within a temperature controlled, humidified incubator. The cells within the dish or bottle exchange gases with the ambient gas atmosphere within the incubator. It is a two dimensional (2-D) technology because cells typically grow on the bottom of the container or on the surface of the media.
2-D cell culture is a suitable approach for most cells and bacteria, and is used for growing solid tumor cells. The approach, however, does not simulate the in vivo conditions experienced by growing solid tumor cells because these cells grow under conditions of elevated interstitial fluid pressures. These pressures are typically equivalent to the pressures within the arterioles that are feeding the tumor's capillary network. In bone tumors, pressures exceeding 50 mmHg (gauge) have been observed. Further, the elevated pressures alter the genetic expressions of tumor cells. Thus when studying the behavior of solid tumor cells, i.e. their response to chemotherapeutic agents, cells grown using the traditional 2-D approach may not reflect the behavior of their in vivo counterparts because of the major differences between the growth conditions.
Attempts to culture cells under elevated pressure environments have utilized elevated gas pressure within the petri dish or culture bottle incubator to achieve the desired pressure. However, the problem with this approach is the growth media's gas content is equilibrated to that of the imposed incubator gas pressure. The dissolved gas content is thus higher than physiologic levels. While tumor interstitial fluid pressures are elevated, the gas content of the fluid is only equilibrated to one atmosphere because that is the pressure within the lung, the organ responsible for gas equilibration.
The cassette is a new approach to 2-D cell culture introduced by BioCrystal, Ltd. It consists of a thin plastic case with two gas permeable membranes and two rubber infusion ports. The cassette permits cell culture under conventional growth conditions in a fully enclosed chamber with rapid gas exchange and cell harvest. Its design, however, is not capable of tolerating the elevated pressures needed to culture tumor cells. Pressurization of the cassette media results in bulging of the membrane sides. The effects of bulging include changing the media volume and membrane thickness as a function of pressure, increasing the membranes' susceptibility to rupture, and increasing the diffusion path for gas exchange within the media.